Konstantin Demin
c3d09a3e94
imported from https://salsa.debian.org/kernel-team/linux.git commit 9d5cc9d9d6501d7f1dd7e194d4b245bd0b6c6a22 version 6.11.4-1
108 lines
3.5 KiB
Diff
108 lines
3.5 KiB
Diff
From: Mike Galbraith <umgwanakikbuti@gmail.com>
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Date: Sat, 27 Feb 2016 08:09:11 +0100
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Subject: [PATCH 1/8] drm/i915: Use preempt_disable/enable_rt() where
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recommended
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.11/older/patches-6.11-rt7.tar.xz
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Mario Kleiner suggest in commit
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ad3543ede630f ("drm/intel: Push get_scanout_position() timestamping into kms driver.")
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a spots where preemption should be disabled on PREEMPT_RT. The
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difference is that on PREEMPT_RT the intel_uncore::lock disables neither
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preemption nor interrupts and so region remains preemptible.
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The area covers only register reads and writes. The part that worries me
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is:
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- __intel_get_crtc_scanline() the worst case is 100us if no match is
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found.
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- intel_crtc_scanlines_since_frame_timestamp() not sure how long this
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may take in the worst case.
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It was in the RT queue for a while and nobody complained.
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Disable preemption on PREEPMPT_RT during timestamping.
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[bigeasy: patch description.]
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Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
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Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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drivers/gpu/drm/i915/display/intel_vblank.c | 38 ++++++++++++++++++++--------
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1 file changed, 28 insertions(+), 10 deletions(-)
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--- a/drivers/gpu/drm/i915/display/intel_vblank.c
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+++ b/drivers/gpu/drm/i915/display/intel_vblank.c
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@@ -303,6 +303,26 @@ int intel_crtc_scanline_to_hw(struct int
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* all register accesses to the same cacheline to be serialized,
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* otherwise they may hang.
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*/
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+static void intel_vblank_section_enter_irqsave(struct drm_i915_private *i915, unsigned long *flags)
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+ __acquires(i915->uncore.lock)
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+{
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+#ifdef I915
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+ spin_lock_irqsave(&i915->uncore.lock, *flags);
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+#else
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+ *flags = 0;
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+#endif
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+}
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+
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+static void intel_vblank_section_exit_irqrestore(struct drm_i915_private *i915, unsigned long flags)
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+ __releases(i915->uncore.lock)
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+{
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+#ifdef I915
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+ spin_unlock_irqrestore(&i915->uncore.lock, flags);
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+#else
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+ if (flags)
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+ return;
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+#endif
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+}
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static void intel_vblank_section_enter(struct drm_i915_private *i915)
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__acquires(i915->uncore.lock)
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{
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@@ -354,10 +374,10 @@ static bool i915_get_crtc_scanoutpos(str
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* timing critical raw register reads, potentially with
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* preemption disabled, so the following code must not block.
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*/
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- local_irq_save(irqflags);
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- intel_vblank_section_enter(dev_priv);
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+ intel_vblank_section_enter_irqsave(dev_priv, &irqflags);
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- /* preempt_disable_rt() should go right here in PREEMPT_RT patchset. */
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+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
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+ preempt_disable();
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/* Get optional system timestamp before query. */
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if (stime)
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@@ -421,10 +441,10 @@ static bool i915_get_crtc_scanoutpos(str
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if (etime)
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*etime = ktime_get();
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- /* preempt_enable_rt() should go right here in PREEMPT_RT patchset. */
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+ if (IS_ENABLED(CONFIG_PREEMPT_RT))
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+ preempt_enable();
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- intel_vblank_section_exit(dev_priv);
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- local_irq_restore(irqflags);
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+ intel_vblank_section_exit_irqrestore(dev_priv, irqflags);
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/*
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* While in vblank, position will be negative
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@@ -462,13 +482,11 @@ int intel_get_crtc_scanline(struct intel
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unsigned long irqflags;
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int position;
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- local_irq_save(irqflags);
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- intel_vblank_section_enter(dev_priv);
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+ intel_vblank_section_enter_irqsave(dev_priv, &irqflags);
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position = __intel_get_crtc_scanline(crtc);
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- intel_vblank_section_exit(dev_priv);
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- local_irq_restore(irqflags);
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+ intel_vblank_section_exit_irqrestore(dev_priv, irqflags);
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return position;
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}
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